Digest::SHA(3perl) Perl Programmers Reference Guide Digest::SHA(3perl)
NAME
Digest::SHA - Perl extension for SHA-1/224/256/384/512
SYNOPSIS
In programs:
# Functional interface
use Digest::SHA qw(sha1 sha1_hex sha1_base64 ...);
$digest = sha1($data);
$digest = sha1_hex($data);
$digest = sha1_base64($data);
$digest = sha256($data);
$digest = sha384_hex($data);
$digest = sha512_base64($data);
# Object-oriented
use Digest::SHA;
$sha = Digest::SHA->new($alg);
$sha->add($data); # feed data into stream
$sha->addfile(*F);
$sha->addfile($filename);
$sha->add_bits($bits);
$sha->add_bits($data, $nbits);
$sha_copy = $sha->clone; # make copy of digest object
$state = $sha->getstate; # save current state to string
$sha->putstate($state); # restore previous $state
$digest = $sha->digest; # compute digest
$digest = $sha->hexdigest;
$digest = $sha->b64digest;
From the command line:
$ shasum files
$ shasum --help
SYNOPSIS (HMAC-SHA)
# Functional interface only
use Digest::SHA qw(hmac_sha1 hmac_sha1_hex ...);
$digest = hmac_sha1($data, $key);
$digest = hmac_sha224_hex($data, $key);
$digest = hmac_sha256_base64($data, $key);
ABSTRACT
Digest::SHA is a complete implementation of the NIST Secure Hash
Standard. It gives Perl programmers a convenient way to calculate
SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, and SHA-512/256
message digests. The module can handle all types of input, including
partial-byte data.
DESCRIPTION
Digest::SHA is written in C for speed. If your platform lacks a C
compiler, you can install the functionally equivalent (but much slower)
Digest::SHA::PurePerl module.
The programming interface is easy to use: it's the same one found in
CPAN's Digest module. So, if your applications currently use
Digest::MD5 and you'd prefer the stronger security of SHA, it's a simple
matter to convert them.
The interface provides two ways to calculate digests: all-at-once, or
in stages. To illustrate, the following short program computes the
SHA-256 digest of "hello world" using each approach:
use Digest::SHA qw(sha256_hex);
$data = "hello world";
@frags = split(//, $data);
# all-at-once (Functional style)
$digest1 = sha256_hex($data);
# in-stages (OOP style)
$state = Digest::SHA->new(256);
for (@frags) { $state->add($_) }
$digest2 = $state->hexdigest;
print $digest1 eq $digest2 ?
"whew!\n" : "oops!\n";
To calculate the digest of an n-bit message where n is not a multiple of
8, use the add_bits() method. For example, consider the 446-bit message
consisting of the bit-string "110" repeated 148 times, followed by "11".
Here's how to display its SHA-1 digest:
use Digest::SHA;
$bits = "110" x 148 . "11";
$sha = Digest::SHA->new(1)->add_bits($bits);
print $sha->hexdigest, "\n";
Note that for larger bit-strings, it's more efficient to use the two-
argument version add_bits($data, $nbits), where $data is in the
customary packed binary format used for Perl strings.
The module also lets you save intermediate SHA states to a string. The
getstate() method generates portable, human-readable text describing the
current state of computation. You can subsequently restore that state
with putstate() to resume where the calculation left off.
To see what a state description looks like, just run the following:
use Digest::SHA;
print Digest::SHA->new->add("Shaw" x 1962)->getstate;
As an added convenience, the Digest::SHA module offers routines to
calculate keyed hashes using the HMAC-SHA-1/224/256/384/512 algorithms.
These services exist in functional form only, and mimic the style and
behavior of the sha(), sha_hex(), and sha_base64() functions.
# Test vector from draft-ietf-ipsec-ciph-sha-256-01.txt
use Digest::SHA qw(hmac_sha256_hex);
print hmac_sha256_hex("Hi There", chr(0x0b) x 32), "\n";
UNICODE AND SIDE EFFECTS
Perl supports Unicode strings as of version 5.6. Such strings may
contain wide characters, namely, characters whose ordinal values are
greater than 255. This can cause problems for digest algorithms such as
SHA that are specified to operate on sequences of bytes.
The rule by which Digest::SHA handles a Unicode string is easy to state,
but potentially confusing to grasp: the string is interpreted as a
sequence of byte values, where each byte value is equal to the ordinal
value (viz. code point) of its corresponding Unicode character. That
way, the Unicode string 'abc' has exactly the same digest value as the
ordinary string 'abc'.
Since a wide character does not fit into a byte, the Digest::SHA
routines croak if they encounter one. Whereas if a Unicode string
contains no wide characters, the module accepts it quite happily. The
following code illustrates the two cases:
$str1 = pack('U*', (0..255));
print sha1_hex($str1); # ok
$str2 = pack('U*', (0..256));
print sha1_hex($str2); # croaks
Be aware that the digest routines silently convert UTF-8 input into its
equivalent byte sequence in the native encoding (cf. utf8::downgrade).
This side effect influences only the way Perl stores the data
internally, but otherwise leaves the actual value of the data intact.
NIST STATEMENT ON SHA-1
NIST acknowledges that the work of Prof. Xiaoyun Wang constitutes a
practical collision attack on SHA-1. Therefore, NIST encourages the
rapid adoption of the SHA-2 hash functions (e.g. SHA-256) for
applications requiring strong collision resistance, such as digital
signatures.
ref. <http://csrc.nist.gov/groups/ST/hash/statement.html>
PADDING OF BASE64 DIGESTS
By convention, CPAN Digest modules do not pad their Base64 output.
Problems can occur when feeding such digests to other software that
expects properly padded Base64 encodings.
For the time being, any necessary padding must be done by the user.
Fortunately, this is a simple operation: if the length of a
Base64-encoded digest isn't a multiple of 4, simply append "="
characters to the end of the digest until it is:
while (length($b64_digest) % 4) {
$b64_digest .= '=';
}
To illustrate, sha256_base64("abc") is computed to be
ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0
which has a length of 43. So, the properly padded version is
ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=
EXPORT
None by default.
EXPORTABLE FUNCTIONS
Provided your C compiler supports a 64-bit type (e.g. the long long of
C99, or __int64 used by Microsoft C/C++), all of these functions will be
available for use. Otherwise, you won't be able to perform the SHA-384
and SHA-512 transforms, both of which require 64-bit operations.
Functional style
sha1($data, ...)
sha224($data, ...)
sha256($data, ...)
sha384($data, ...)
sha512($data, ...)
sha512224($data, ...)
sha512256($data, ...)
Logically joins the arguments into a single string, and returns its
SHA-1/224/256/384/512 digest encoded as a binary string.
sha1_hex($data, ...)
sha224_hex($data, ...)
sha256_hex($data, ...)
sha384_hex($data, ...)
sha512_hex($data, ...)
sha512224_hex($data, ...)
sha512256_hex($data, ...)
Logically joins the arguments into a single string, and returns its
SHA-1/224/256/384/512 digest encoded as a hexadecimal string.
sha1_base64($data, ...)
sha224_base64($data, ...)
sha256_base64($data, ...)
sha384_base64($data, ...)
sha512_base64($data, ...)
sha512224_base64($data, ...)
sha512256_base64($data, ...)
Logically joins the arguments into a single string, and returns its
SHA-1/224/256/384/512 digest encoded as a Base64 string.
It's important to note that the resulting string does not contain
the padding characters typical of Base64 encodings. This omission
is deliberate, and is done to maintain compatibility with the family
of CPAN Digest modules. See "PADDING OF BASE64 DIGESTS" for
details.
OOP style
new($alg)
Returns a new Digest::SHA object. Allowed values for $alg are 1,
224, 256, 384, 512, 512224, or 512256. It's also possible to use
common string representations of the algorithm (e.g. "sha256",
"SHA-384"). If the argument is missing, SHA-1 will be used by
default.
Invoking new as an instance method will reset the object to the
initial state associated with $alg. If the argument is missing, the
object will continue using the same algorithm that was selected at
creation.
reset($alg)
This method has exactly the same effect as new($alg). In fact,
reset is just an alias for new.
hashsize
Returns the number of digest bits for this object. The values are
160, 224, 256, 384, 512, 224, and 256 for SHA-1, SHA-224, SHA-256,
SHA-384, SHA-512, SHA-512/224 and SHA-512/256, respectively.
algorithm
Returns the digest algorithm for this object. The values are 1,
224, 256, 384, 512, 512224, and 512256 for SHA-1, SHA-224, SHA-256,
SHA-384, SHA-512, SHA-512/224, and SHA-512/256, respectively.
clone
Returns a duplicate copy of the object.
add($data, ...)
Logically joins the arguments into a single string, and uses it to
update the current digest state. In other words, the following
statements have the same effect:
$sha->add("a"); $sha->add("b"); $sha->add("c");
$sha->add("a")->add("b")->add("c");
$sha->add("a", "b", "c");
$sha->add("abc");
The return value is the updated object itself.
add_bits($data, $nbits)
add_bits($bits)
Updates the current digest state by appending bits to it. The
return value is the updated object itself.
The first form causes the most-significant $nbits of $data to be
appended to the stream. The $data argument is in the customary
binary format used for Perl strings.
The second form takes an ASCII string of "0" and "1" characters as
its argument. It's equivalent to
$sha->add_bits(pack("B*", $bits), length($bits));
So, the following two statements do the same thing:
$sha->add_bits("111100001010");
$sha->add_bits("\xF0\xA0", 12);
Note that SHA-1 and SHA-2 use most-significant-bit ordering for
their internal state. This means that
$sha3->add_bits("110");
is equivalent to
$sha3->add_bits("1")->add_bits("1")->add_bits("0");
addfile(*FILE)
Reads from FILE until EOF, and appends that data to the current
state. The return value is the updated object itself.
addfile($filename [, $mode])
Reads the contents of $filename, and appends that data to the
current state. The return value is the updated object itself.
By default, $filename is simply opened and read; no special modes or
I/O disciplines are used. To change this, set the optional $mode
argument to one of the following values:
"b" read file in binary mode
"U" use universal newlines
"0" use BITS mode
The "U" mode is modeled on Python's "Universal Newlines" concept,
whereby DOS and Mac OS line terminators are converted internally to
UNIX newlines before processing. This ensures consistent digest
values when working simultaneously across multiple file systems.
The "U" mode influences only text files, namely those passing Perl's
-T test; binary files are processed with no translation whatsoever.
The BITS mode ("0") interprets the contents of $filename as a
logical stream of bits, where each ASCII '0' or '1' character
represents a 0 or 1 bit, respectively. All other characters are
ignored. This provides a convenient way to calculate the digest
values of partial-byte data by using files, rather than having to
write separate programs employing the add_bits method.
getstate
Returns a string containing a portable, human-readable
representation of the current SHA state.
putstate($str)
Returns a Digest::SHA object representing the SHA state contained in
$str. The format of $str matches the format of the output produced
by method getstate. If called as a class method, a new object is
created; if called as an instance method, the object is reset to the
state contained in $str.
dump($filename)
Writes the output of getstate to $filename. If the argument is
missing, or equal to the empty string, the state information will be
written to STDOUT.
load($filename)
Returns a Digest::SHA object that results from calling putstate on
the contents of $filename. If the argument is missing, or equal to
the empty string, the state information will be read from STDIN.
digest
Returns the digest encoded as a binary string.
Note that the digest method is a read-once operation. Once it has
been performed, the Digest::SHA object is automatically reset in
preparation for calculating another digest value. Call
$sha->clone->digest if it's necessary to preserve the original
digest state.
hexdigest
Returns the digest encoded as a hexadecimal string.
Like digest, this method is a read-once operation. Call
$sha->clone->hexdigest if it's necessary to preserve the original
digest state.
b64digest
Returns the digest encoded as a Base64 string.
Like digest, this method is a read-once operation. Call
$sha->clone->b64digest if it's necessary to preserve the original
digest state.
It's important to note that the resulting string does not contain
the padding characters typical of Base64 encodings. This omission
is deliberate, and is done to maintain compatibility with the family
of CPAN Digest modules. See "PADDING OF BASE64 DIGESTS" for
details.
HMAC-SHA-1/224/256/384/512
hmac_sha1($data, $key)
hmac_sha224($data, $key)
hmac_sha256($data, $key)
hmac_sha384($data, $key)
hmac_sha512($data, $key)
hmac_sha512224($data, $key)
hmac_sha512256($data, $key)
Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with
the result encoded as a binary string. Multiple $data arguments are
allowed, provided that $key is the last argument in the list.
hmac_sha1_hex($data, $key)
hmac_sha224_hex($data, $key)
hmac_sha256_hex($data, $key)
hmac_sha384_hex($data, $key)
hmac_sha512_hex($data, $key)
hmac_sha512224_hex($data, $key)
hmac_sha512256_hex($data, $key)
Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with
the result encoded as a hexadecimal string. Multiple $data
arguments are allowed, provided that $key is the last argument in
the list.
hmac_sha1_base64($data, $key)
hmac_sha224_base64($data, $key)
hmac_sha256_base64($data, $key)
hmac_sha384_base64($data, $key)
hmac_sha512_base64($data, $key)
hmac_sha512224_base64($data, $key)
hmac_sha512256_base64($data, $key)
Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with
the result encoded as a Base64 string. Multiple $data arguments are
allowed, provided that $key is the last argument in the list.
It's important to note that the resulting string does not contain
the padding characters typical of Base64 encodings. This omission
is deliberate, and is done to maintain compatibility with the family
of CPAN Digest modules. See "PADDING OF BASE64 DIGESTS" for
details.
SEE ALSO
Digest, Digest::SHA::PurePerl
The Secure Hash Standard (Draft FIPS PUB 180-4) can be found at:
<http://csrc.nist.gov/publications/drafts/fips180-4/Draft-FIPS180-4_Feb2011.pdf>
The Keyed-Hash Message Authentication Code (HMAC):
<http://csrc.nist.gov/publications/fips/fips198/fips-198a.pdf>
AUTHOR
Mark Shelor <mshelor@cpan.org>
ACKNOWLEDGMENTS
The author is particularly grateful to
Gisle Aas
H. Merijn Brand
Sean Burke
Chris Carey
Alexandr Ciornii
Chris David
Jim Doble
Thomas Drugeon
Julius Duque
Jeffrey Friedl
Robert Gilmour
Brian Gladman
Jarkko Hietaniemi
Adam Kennedy
Mark Lawrence
Andy Lester
Alex Muntada
Steve Peters
Chris Skiscim
Martin Thurn
Gunnar Wolf
Adam Woodbury
"who by trained skill rescued life from such great billows and such
thick darkness and moored it in so perfect a calm and in so brilliant a
light" - Lucretius
COPYRIGHT AND LICENSE
Copyright (C) 2003-2022 Mark Shelor
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perlartistic
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